The present invention relates generally to improvements in coking ovens and specifically to the provision of apparatus for partially drying and preheating wet coal before feeding thereof to the coking oven utilizing intermediate temperature flue gases that have heretofore been used to preheat the combustion air for the coke oven, thereby to produce coke with a high stability index at a fuel savings with high coking productivity.
Coking systems have been provided heretofore utilizing flue gases to preheat the coal being fed through the coke ovens, and examples thereof are illustrated in U.S. Pat. No. 1,827,483 granted Oct. 13, 1931 to S. W. Parr et al.; U.S. Pat. No. 1,899,887 granted Feb. 28, 1933 to E. W. Thiele; U.S. Pat. No. 2,552,014 granted May 8, 1951 to F. Puening; and U.S. Pat. No. 3,013,951 granted Dec. 19, 1961 to V. Mansfield.
The Parr et al. U.S. Pat. No. 1,827,483 and the Thiele U.S. Pat. No. 1,899,887 both use high temperature flue gases directly from the coking retort, or from burning a portion of the coke, to preheat the incoming coal to a high temperature which will render the coke bone-dry and almost at the plastic stage thereof. Coal that has been heated to a bone-dry condition presents an explosion hazard due to the extremely fine coal dust that is accompanied thereby. Furthermore, coal at these high temperatures is hard to handle since the individual pieces of coal tend to cling to each other and to the walls of containers and devices used to convey the dried coal to the coke oven. In the present invention, the high temperature flue gases directly from the coking operation are first used to preheat the air for the combustion chamber thus reducing the flue gases to an intermediate temperature, and the flue gases at the intermediate temperature are then used to partially dry the coal to a water content from about 2% to about 5% by weight and to a temperature in the range from about 130.degree. F. to about 190.degree. F. This eliminates the explosion hazard from dry coal dust and also eliminates any tendency of the preheated coal to cling one piece to the other and to the walls of containers and devices used to convey the partially dried coal to the coke oven.
The Puening U.S. Pat. No. 2,552,014 shows a three-stage coal preheater which heats the coal to a bone-dry condition at a temperature of about 500.degree. F. As has been pointed out above, coal that has been heated to a bone-dry condition presents an explosion hazard due to the extremely fine coal dust that is accompanied thereby. Furthermore, coal at a high temperature is hard to handle since the individual pieces of coal tend to cling to each other and to the walls of containers and devices used to convey the dried coal to the coke oven. By contrast, the present apparatus and method heats the coal to a partially dried condition at a moderate temperature so as to overcome these problems.
The Mansfield U.S. Pat. No. 3,013,951 shows a continuous coking apparatus wherein flue gases are used directly to preheat the coal to a bone-dry condition at a temperature of 350.degree. F. to 450.degree. F. Coal thus heated to a bone-dry condition presents an explosion hazard due to the extremely fine coal dust that accompanies such dried coal. Furthermore, coal at these high temperatures is hard to handle since the individual pieces of coal tend to cling to each other and to the walls of containers and devices used to convey the dried coal to the coke oven. The apparatus and method of the present invention overcomes these problems by only partially drying the coal and heating the coal to a low temperature no greater than about 190.degree. F. so that there is no tendency of the coal to cling to the walls of containers and devices used to convey the dried coal to the coke oven.
There is reported in an article entitled "Heat Drying Coals at Moderate Temperatures Before Coking" by H. W. Jackman and R. J. Helfinstine, Circular No. 449, dated 1970, issued by the Illinois State Geological Survey, a report of the effect of drying coals on the coking thereof. There is no suggestion in this article, however, of utilizing intermediate temperature flue gasses from a coking oven to partially dry and preheat coal as taught in the present invention.